Z-axis only moving into one direction. need help

at the moment, I'm building my own Wooden-RepStrap.
But now I've a little (I hope so) problem: my z-axis is only moving into one direction.

I'm using the Techzone electronics with the newest RepRap Firmware.
If I swap the z-axis cable with the y-axis cable at the motherboard, the problem occur at the y-axis.
So I think its not a problem with the stepper controller or the cables.

I tried also the ReplicatorG soft- and firmware, but the Problem still there.